A domestic co-generation (microCHP) unit uses a Stirling engine, a burner and an alternator to produce both electricity and heat for water and/or space heating. A microCHP typically comprises at least one water pump and at least one fan which circulate cooling water and air through the engine during operation, and which are typically powered from the mains supply. If mains power is removed when the engine is (or has recently been) running, the water pump and fan providing both the required types of cooling also immediately shut down. The mains power supply to the microCHP may cease due to a consumer's prepaid power credit running out for example.
International PCT patent application publication WO 03/076857 discloses a domestic combined heat and power unit with an additional power supply situated within a grid independent module. This power supply is used to start the microCHP in the absence of mains supply. The power supply is a battery for example, and is used only for supplying the control means, the ignitor and the pulse generator.